About 50% of the glycoprotein N-asparagine linked carbohydrate groups of cultured chicken and human fibroblasts are of the oligomannosyl (high mannose) type. These molecules are found in the cell surface with carbohydrate exposed to the cell environment. In both species there are at least five different oligomannosyl glycopeptides whose quantity and specific structure show marked alterations with malignancy and cell growth status. We have purified these substances in chemical amounts from cells and from Sindbis virus and Semliki Forest virus grown in cells in various physiological states (density-inhibited, rapidly growing, cancer cells) and determined structures by high-field 1H nuclear magnetic resonance spectroscopy, gas-liquid chromatography, methylation analyses and specific glycosidase digestion. We have shown that the degree of processing of these carbohydrates is growth dependent, and we will seek the specific glycosidase (mannosidase) which is involved. Other studies are utilizing viruses in order to understand how the expression of membrane glycoproteins at the cell surface is regulated.